By way of examples, reference can be made to the patent applications in France published under the following numbers: 2 767 851, 2 751 682, 2 734 296, 2 712 006, 2 707 708, 2 703 711, 2 699 211, 2 699 209, 2 695 670, 2 691 193, 2 688 849, 2 685 036, 2 645 135, 2 630 476, 2 627 207, 2 624 167, 2 623 540, 2 619 531, 2 597 906, 2 611 779, 2 592 416, 2 587 447, 2 561 690, 2 587 392, 2 552 473, 2 537 112, 2 531 012, 2 524 922, 2 475 093, 2 486 127, 2 523 622, 2 310 450, 2 270 407, 2 202 997, 2 175 854, 2 145 147, 2 106 407, 2 078 579, 2 002 261, 1 475 446, 1 303 930, 1 287 077.
By way of examples, reference can also be made to the following documents: U.S. Pat. Nos. 5,058,340, 4,083,157, EP-A-643 180, EP-A-652 339, EP-A-588 748, EP-A-504 530, EP-A-338 925, EP-A-281 468, EP-A-215 715, EP-A-089 905, EP-A-043 466, WO-A-94/12741, WO-A-92/18722.
Reference can further be made to the following patent applications in France originating from the Applicant: 2 736 615, 2 756 600, 2 727 711, 2 712 325, 2 699 613, 2 695 670, 2 692 302, 2 658 849.
The materials known in the prior art for manufacturing false stretched ceilings or walls are most often polymers provided with a large number of qualities such as in particular fire resistance, air tightness, that is being dust-proof and damp-proof, and ease of maintenance.
False ceilings obtained by means of such materials can incorporate heat insulants, spot lights or various lighting elements, as well as ventilation or aeration openings or sprinklers.
As said false ceilings are dismountable, any intervention can be made in the plenum chamber of an air heater.
The polymers for stretched ceilings known in the prior art, regardless of whether they are translucid or opaque, possibly mass-tinted, matt, lacquered, marbled, suede or satin lustre, can thus be used both in an industrial and hospital environment, for collective equipment, laboratories or dwellings.
The lacquered finishing makes it possible to obtain a mirror effect used in shopping centres, a matt finishing appearing similar to a plaster aspect being most usually used for conventional decorations.
In a prior technique, the stretched fabrics or sheets on the roof or wall were definitively fixed by means of points or staples.
The conventional stretched false ceilings currently include:                firstly, a horizontal frame fixed onto the upper portion of the walls of a room, said frame being an external rail formed by sections joined end to end,        secondly, a web stretched horizontally inside said frame.        
This arrangement enables the stretched ceiling to be dismantled.
Keeping the web in place with respect to the rail frame is obtained by various means, some examples of same being given below.
According to a first type of embodiment, the rail comprises a U-shaped groove defined by two walls, one of the two walls having a lip orientated towards the bottom of the groove, hooks being placed on the periphery of the web positively being anchored on this lip.
As regards this first type of embodiment, reference can be made to the document FR-A-1 303 930.
According to a second type of embodiment, the rail includes an U-shaped groove defined by two walls, one of the latter comprising a shoulder having one portion situated towards the bottom of groove to form a stop.
As regards this second type of embodiment, reference can be made for example to the documents FR-A-1 475 446, FR-A-2 002 261.
According to a third type of embodiment, the rail is a flat section, the web being squeezed between said section and the wall on which said section is fixed.
As regards said third type of embodiment, reference can be made for example to the document FR-A-2 734 296.
According to a fourth type of embodiment, the rail is provided with means forming a fitting and tension clamp.
As regards this fourth type of embodiment, reference can be made for example to the documents FR-A-2 699 211 and FR-A-2 537 112.
According to a fifth type of embodiment, the rail is provided with a groove to which hook-shaped elements cling in the way of a fish-hook and integral with the web.
As regards this fifth type of embodiments, reference can be made for example to the documents FR-A-2 630 476, EP-A-388 925.
Within the context of stretched ceilings of the prior art, regardless of means used for maintaining tension of the web on the rail frame (stops, cramps, fish-hooks, clamping, latching . . . ) the rails are conventionally made of extruded polymer or an aluminium alloy.
The stretched false ceilings are moreover mostly mounted with the web fully stretched horizontally.
In certain particular embodiments, as the web is stretched on a horizontal rail frame fixed to the walls of a room, deformations of the stretched web occur, as described in the documents FR-A-1 515 260 or EP-A-281 468.
Considering that in certain embodiments the stretched ceilings had the drawback of showing the lower portion of the rail used to fix them, certain installers have offered the use of complex sections only partially masking said rail.
Thus, for example, the document EP-A-338 925 describes a rail comprising a recess defined by two vertical wings of different heights, namely a first wing of smaller height terminating towards the bottom by a shoulder extending horizontally in the direction of the second wing, and a second wing of greater height; a “fish-hook” integral with the edge of a fabric able to be engaged between the two wings so as to take support on the shoulder of the first wing, said fabric of the stretched ceiling thus being deviated upwards so as to penetrate into the recess whilst taking support and being deviated against the lower extremity of the second wing.
As specified in said prior document, a clip or finishing cover is provided to cover the lower portion of the rail. In other words, the complex section described in the document EP-338 925 remains visible as long as a finishing cover is not installed, which proves to be a long and tedious operation.
The document FR-2 619 531 describes in relation to a false ceiling or stretched false wall a rigid PVC rail provided with a recess defined by two vertical wings of different heights, namely a first wing of small height next to a wall and ending towards the bottom by a mobile perforated tongue extending in an oblique direction towards the higher second wing; a fish-hook integral with the edge of a fabric able to be engaged between the two wings so as to take support both on the second wing and the perforated mobile tongue, said fabric of the stretched ceiling being thus deviated upwards so as to penetrate inside the recess by coming to rest and being deviated against the lower extremity of the second wing.
The rail described in the document FR-A-2 619 531 has a large number of drawbacks. In particular, it remains visible after it has been mounted. Having regard to its small tapered section, the mobile tongue does not allow the fish-hook to be properly held in place. Increasing the tongue section would a priori reduce this problem but would make it more difficult to place the forked-tie.
The document FR-A-2 597 906 describes, as regards a false ceiling or a false stretched wall, a rail provided with a recess defined by two vertical wings of different heights, namely a first wing of very small height close to a wall and a second wing of greater height; a forked-tie integral with the edge of a fabric able to be engaged between said two wings so as to fasten onto the second wing, said fabric of the stretched ceiling being thus deviated upwards so as to penetrate inside the recess whilst taking support and being deviated against the lower extremity of the second wing.
The rail described in the document FR-A-2 597 906, just like those of the documents FR-A-2 619 531 or EP-A-338 925, remains visible and, so as to mask the slit formed between the edge of the fabric and the wall on which the rail is fixed, a finish profile needs to be provided.